The normal concentration of glucose in the body is 3-7 millimoles per liter, and unless the concentration is regulated to within this normal range, there can be long term complications in the body leading for example to blindness.
For non-diabetics, this regulation is controlled automatically by an enzyme in the body. Diabetics, on the other hand, lack this enzyme and must therefore resort to use of a carefully controlled diet or, in some cases, the use of insulin injections.
Reflectometers have already been developed to determine the glucose content of a blood sample. The sample is taken and transferred to a test stick containing reagents including an enzyme which, indirectly, reacts with the glucose of the blood to change the colour of a dye. The greater the glucose content, the deeper becomes the colour of the dye. After a fixed period, the bood is washed or wiped off the test stick, and the stick is inserted into the reflectometer to provide a reading dependent on the colour of the dye.
Sophisticated reflectometers which include glass components such as prisms and mirrors would be too expensive for this type of application where accuracy need not be greater than about .+-.0.5 millimoles per liter. Attempts to produce a simple, inexpensive reflectometer have therefore been made. However, these meters are still rather bulky and difficult to use and are not therefore suitable for use by a diabetic at home. For example, one such meter requires a two-stage calibration each time the meter is used. It also relies upon the movement of a pointer over a graduated non-linear scale to provide its readout. Moreover, the test stick is inserted in a hinged cover which, as it closes, trips a microswitch to switch on the meter, and we have found that different readings can be obtained for the same sample depending on the point at which the cover is pressed to trip the microswitch. A need therefore exists for a more convenient and reliable meter.